Rotary type grounding switch

ABSTRACT

A two-piece shaft, having a spring contact attached thereto, extends through an apparatus casing and through an index plate. A handle is attached to the shaft and has mounted thereon a spring loaded plunger assembly which locks the handle into position. The spring contact, which is grounded, is rotated when the handle is rotated. When the handle is locked in the operating position, the switch is open. When the handle is locked in the grounded position, the spring contact touches a terminal stud which is connected to the output circuit of the electrical apparatus, thus grounding the output circuit.

8 United States Patent 1 1 11 1 3,742,353

Bell et al. June 26, 1973 [54] ROTARY TYPE GROUNDING SWITCH 3,030,460 4/l962 l-luetten et al. 200/11 G Inventors: Kenneth B. Frederick J Brut; 3,467,794 9/1969 Ristuccla 200/166 J X gifonso J. Mazanek, all of Sharon, m y g r R Scott Attorney-A. T. Stratton, and F. E. Browder [73] Assignee: Westinghouse Electric Corporation,

Pittsburgh, Pa. [57] ABSTRACT 22 Filed; Sept, 9, 1971 A two-piece shaft, having a spring contact attached thereto, extends through an apparatus casing and [211 App! 179079 through an index plate. A handle is attached to the shaft and has mounted thereon a spring loaded plunger 52 us. c1. 200/11 G, 200/17 R, 200/166 J assembly which locks the handle into Position The 51 1m. 01. H01h 19/20 p g Contact, which is grounded, is rotated when the [58] Field of Search 200/1 R, 6 R, 6 c, handle is rotated- When the handle is locked in the p- 200 11 G, 11 K, 17 17 B, 1 J 1 9 R crating position, the switch is open. When the handle is locked in the grounded position, the spring contact 56] Refe en Cit d touches a terminal stud which is connected to the out- UNITED STATES PATENTS put circuit of the electrical apparatus, thus grounding the output circuit. 3,484,567 12/1969 Johnson 200/11 G 2,751,449 6/1956 Krahulec et al. 200/ 11 G 3 Claims, 3 Drawing Figures PATENIEUJms 1975 INSULATIVE SHAFT FIG.3

1 ROTARY TYPE GROUNDING SWITCH BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates, in general, to electrical apparatus and, more specifically, to grounding switches for rectifier units associated with power transformers.

2. Description of the Prior Art Rectifier and transformer apparatus associated with direct current load devices usually have a grounding switch arrangement for safety purposes. The gounding switch shorts the output terminal of the rectifier to ground when the load device is being repaired, adjusted or cleaned. The workman, after deenergizing the transformer, closes the grounding switch before starting work on the apparatus. The main purpose of such a switch is to prevent DC potential from being accidentally applied to the load device, which may be an electrostatic precipitator. This safety feature is required by industry standards governing such equipment and reduces the harmful effects of accidentally energizing a transformer while the precipitator is being worked on. A secondary purpose of the grounding switch is to bleed off any charge which exists on the precipitator apparatus after the transformer is deenergized.

It is sometimes required that the transformer and rectifier apparatus be connected in a full-wave configuration. At other times, it may be required to operate the apparatus in a half-wave configuration or in a voltage doubler configuration.

Grounding switches used with such apparatus must be capable of grounding DC output voltage in all modes of operation, thus it is necessarily complex. Such a switch is described in US. Pat. No. 3,029,579, which is assigned to the same assignee as this invention.

In certain specific applications, only full-wave rectification is required. Therefore, it is desirable, and it is an object of this invention, to provide a grounding switch for full-wave rectifier apparatus which can be constructed more economically than prior art grounding switches.

SUMMARY OF THE INVENTION An index plate is attached to a portion of the casing structure. A shaft projects through an opening in the index plate and is attached to a handle. The handle is used to rotate the shaft and may be locked into either of two switch positions by a plunger assembly which projects into an opening in the index plate corresponding to that switch position. The shaft which is connected to the handle is attached to an insulated shaft having a spring contact mounted thereon. When the handle is locked in one position, the spring contact does not touch a terminal stud which is connected to the output of the rectifier apparatus. When the handle is locked in the other position, the spring contact touches the terminal stud. The spring contact is connected to ground by a flexible current-conducting lead, thus the terminal stud and the rectifier apparatus output is grounded.

BRIEF DESCRIPTION OF THE DRAWINGS Further advantages and uses of this invention will become more apparent when considered in view of the following detailed description and drawing, in which:

FIG. I is an electrical schematic diagram of an electrostatic precipitator powered by a full-wave rectifier circuit which is protected by a grounding switch constructed as taught by this invention;

FIG. 2 is a cutaway view showing a grounding switch constructed according to the teachings of this invention; and

FIG. 3 is a partial sectional view of the grounding switch shown in FIG. 2 taken along the line IIIIII.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Throughout the following description, similar reference characters refer to similar members in all figures of the drawing.

Referring now to the drawing, and FIG. 1 in particu* lar, there is shown a transformer having a primary winding 10, a laminated magnetic core 12, and a secondary winding 14. An AC generator 16 is connected to the primary winding 10 and a rectifier circuit 18 is connected to the secondary winding 14. Although other types of loads may be connected to the rectifier circuit 18, an electrostatic precipitator 20 is illustrated. A grounding switch 22 is connected between the DC potential terminal 24 and ground potential. When the grounding switch 22 is closed, voltage cannot be applied to the precipitator 20.

Although shown connected in a full-wave arrangement, the rectifier circuit 18 may be connected in other arrangements. The diodes 25, 26, 28 and 30 may be single solid state rectifying elements or a stack or series combination of such elements. Other types of rectifying elements may be used within the contemplation of this invention.

FIG. 2 illustrates, in a cutaway view, a casing structure 32 with the ground switch 22 mounted thereto. Although the casing structure 32 may house only the grounding switch 22, or the grounding switch 22 and the rectifier circuit 14, usual practice is for the casing structure 32 to house the grounding switch 22,the rectifier circuit 18, and the power transformer 12. A liquid dielectric and coolant may also be contained within the casing structure 32, with a surface level sufficient to' surround the contact structures of the grounding switch 22. The use of gas dielectrics is also within the conternplation of this invention. An index plate 34 is mounted outside of the casing structure 32. A position indicating plate 35 is attached to the index plate 34 to provide an indication of the position of the handle 36. The vertical portion 38 of the index plate 34 may provide means for attaching interlocking devices. These interlocking devices, by engaging with the handle plate 40, prevent closing the grounding switch 22 while the rectifier circuit I8 is operating.

The index plate 34 is secured by the bolts 42. The handle 36, in the embodiment shown, may be moved to two different positions and is illustrated in the full-wave position. The index plate 34 contains an opening for each position of the switch, such as the opening '44 for the ground position. A plunger assembly 45 is inserted into one of the openings, such as the opening 44, to lock the handle 36 into position. Moving the handle 36 moves the spring contact 46. The spring contact 46 includes a contact member 48 which is constructed .of a suitable material, such as spring steel or copper. A backing plate 50 provides additional support for the contact member 48 and furnishes a reinforced structure in the region where the contact member 48 is attached to the shaft 52 by the bolts 54. A flexible currentconducting lead 56 is attached to the spring contact 46 and to ground potential.

The supporting members 58 and 60 may be part of the supporting structure of the rectifier 18. The cross member 62 is constructed of an insulating material and is attached between the supporting members 58 and 60 by suitable means. A substantially circular opening 64 is positioned in the cross member 62 directly below the shaft 52. The shaft 52 is constructed of an insulating material and has a substnatially rectangular crosssection. The shaft projection 66 extends into the opening 64 to allow the shaft 52 to rotate without excessive movement in a sideways direction.

A terminal stud 68 is secured to the cross member 62 and is electrically connected to the rectifier output circuit by the lead 70. The terminal stud 68 is constructed of a conducting material, such as copper, and is positioned on the cross member 62 so that it engages with the spring contact 46 when the handle 36 is locked in the ground position. The ground position of the handle 36 is such that the spring contact 46 is bent, thereby exerting force between the contact area of the terminal stud 68 and the contact member 48. The fullwave position of the handle 36 is such that the clearance between the terminal stud 68 and the contact member 48 is sufficient to prevent arcing or corona at the rated voltage of the apparatus.

FIG. 3 is a partial sectional view taken along the line IlIlIl of FIG. 2. A boss 72 is attached to the casing structure 32 by a suitable method, such as welding. The boss 72 contains an opening 74 through which the shaft 76 extends. The boss 72 contains a spring 78 and a gasket 80 which are concentrically positioned around the shaft 76 to seal the casing structure 32. The gasket 80 is compressed by the spring 78 to produce a tight fit. The handle boss 82 is attached to the shaft 76 by the pin 84. The plunger 45 is spring loaded to force the lower portion 47 of the plunger 45 into an opening of the index plate 34 to lock the handle 36 into position. The handle 36 is moved from one position to the other by lifting the plunger 45, moving the handle 36, and releasing the plunger so that it may project through the opening in the index plate 34 which corresponds to the new handle position.

The shafts 76 and 52 are attached to each other by the connector 82. The connector 82 is permanently attached to the shaft 76v and has a cavity 84 which is shaped to receive the upper end of the shaft 52. Since the shaft 52 is substantially rectangular in cross section, the connector 82 is similarly shaped to transfer the rorational torque from the shaft 76 to the shaft 52. Both shafts may be permanently attached to the connector 82, however, certain advantages exist if the shaft 52 is simply telescoped into the connector 82. The casing 32, which may be part of a lid or cover, may be raised to open the apparatus. With the embodiment shown, the shafts will separate at the connector 82 to permit ready access to the inner components of the apparatus.

There has been disclosed a new and useful apparatus for grounding the output of electrical apparatus. Since numerous changes may be made in the above described apparatus and different embodiments of the invention may be made without departing from the spirit thereof, it is intended that all of the matter contained in the foregoing description, or shown in the accompanying drawings, shall be interpreted as illustrative rather than limiting.

We claim as our invention 1. A grounding switch for electrical apparatus comprising a boss member adapted for connection to a casing structure, an index plate attached to said boss member, a first shaft extending through an opening in said boss member and an opening in said index plate, handle means attached to said first shaft, locking means for holding said handle means in first and second positions, a second shaft having upper and lower portions, said second shaft being constructed of an insulating material, the upper portion of said second shaft being attached to said first shaft by means which permits the shafts to be disengaged when the casing structure is moved away from said second shaft, a spring contact constructed from resilient metallic material, said contact being attached to the lower end of said second shaft, said spring contact being electrically connected to ground potential, a member rotatably attached to the lower end of said second shaft, a terminal stud mounted on said member in such a location that said spring contact makes contact with said terminal'stud when said handle is locked in the second position and breaks contact with said terminal stud when said handle is locked in the first position.

2. The grounding switch of claim ll including a sealing means for providing a fluid tight seal between the first shaft and the opening in the boss member through which the first shaft extends.

3. The grounding switch of claim 1 wherein index plate contains an opening for each locked position for the handle member, and the locking means comprises a plunger means which is attached to the handle member, said plunger means including resilient means for forcing the plunger into an opening in the index plate. 

1. A grounding switch for electrical apparatus comprising a boss member adapted for connection to a casing structure, an index plate attached to said boss member, a first shaft extending through an opening in said boss member and an opening in said index plate, handle means attached to said first shaft, locking means for holding said handle means in first and second positions, a second shaft having upper and lower portions, said second shaft being constructed of an insulating material, the upper portion of said second shaft being attached to said first shaft by means which permits the shafts to be disEngaged when the casing structure is moved away from said second shaft, a spring contact constructed from resilient metallic material, said contact being attached to the lower end of said second shaft, said spring contact being electrically connected to ground potential, a member rotatably attached to the lower end of said second shaft, a terminal stud mounted on said member in such a location that said spring contact makes contact with said terminal stud when said handle is locked in the second position and breaks contact with said terminal stud when said handle is locked in the first position.
 2. The grounding switch of claim 1 including a sealing means for providing a fluid tight seal between the first shaft and the opening in the boss member through which the first shaft extends.
 3. The grounding switch of claim 1 wherein index plate contains an opening for each locked position for the handle member, and the locking means comprises a plunger means which is attached to the handle member, said plunger means including resilient means for forcing the plunger into an opening in the index plate. 